™Selling 100 shares at a $1,000 loss and buying 40 matched replacements inside the window can disallow $400 of that loss in a simplified taxable-account example.
Taxes & Account Rules
Wash sale
A U.S. tax rule that can disallow a current loss when substantially identical stock or securities are acquired within the specified window.
Plain-English context
Put the definition to work.
A disallowed taxable-account loss is generally preserved in matched basis; an IRA replacement can have different treatment.
Further reading and verification. Examples are hypothetical, not current quotes or recommendations. Product terms, tax treatment and market rules can change. IRS Publication 550 — investment income and expenses